ZFS: unlimited arc cache growth?

[Ivan Voras]

Alexander Leidinger wrote:
> Hi,
> 
> to fs@, please CC me, as I'm not subscribed.
> 
> I monitored (by hand) a while the sysctls kstat.zfs.misc.arcstats.size
> and kstat.zfs.misc.arcstats.hdr_size. Both grow way higher (at some
> point I've seen more than 500M) than what I have configured in
> vfs.zfs.arc_max (40M).
> 
> After a while FS operations (e.g. pkgdb -F with about 900 packages... my
> specific workload is the fixup of gnome packages after the removal of
> the obsolete libusb port) get very slow (in my specific example I let
> the pkgdb run several times over night and it still is not finished).
> 
> The big problem with this is, that at some point in time the machine
> reboots (panic, page fault, page not present, during a fork1). I have
> the impression (beware, I have a watchdog configured, as I don't know if
> a triggered WD would cause the same panic, the following is just a
> guess) that I run out of memory of some kind (I have 1G RAM, i386, max
> kmem size 700M). I restarted  pkgdb several times after a reboot, and it
> continues to process the libusb removal, but hey, this is anoying.
> 
> Does someone see something similar to what I describe (mainly the growth
> of the arc cache way beyond what is configured)? Anyone with some ideas
> what to try?

What you've come across is probably *the* single most important problem
with ZFS - unfortunately not yet resolved. If ARC could be constrained
or removed, other issues would probably be forgivable :)


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